1. Field of the Invention
The invention relates to compositions and methods for aiding the extraction of an emulsified oil from an oil and water emulsion.
2. Description of the Related Art
Most commercial corn oil is produced by front end fractionation of corn germ during the wet mill corn process. Recently, a new source of corn oil has arisen as a by-product of the dry-mill process used in the ethanol industry. Dry milling is a process requiring less energy and less capital investment than wet-milling. Though corn oil captured at the tail-end of a dry mill process is not suitable for food use, it can be used as a biodiesel feedstock.
In the dry-mill ethanol process, yellow dent corn is milled, liquefied and sent to a fermenter. Enzymes and yeast are added to convert starch into ethanol, which is subsequently distilled off. This leaves a slurry called whole stillage. Whole stillage, which contains a concentrated oil fraction, is then separated via centrifugation into liquid and solid fractions called thin stillage and wet cake respectively. While part of the thin stillage is recycled to help liquefy the milled corn, the rest is concentrated via evaporation into thick stillage (or syrup), which is dried and mixed with the wet cake to form distillers' dried gains with solubles (DDGS). This is sold as cattle feed and is a good source of protein.
Due to the concentrating effect dry-milling has on the oil fraction, corn oil extracted from thick stillage has become a profitable co-product for the ethanol industry. Although removing corn oil lowers the energy density of DDGS, some studies suggest that high oil content in DDGS interferes with milk production in dairy cattle, and leads to undesirable pork bellies in swine. Therefore, removing some of the oil not only leads to a valuable co-product, but also may improve DDGS quality.
Current methods of extracting corn oil from thick stillage include solvent extraction (often hexane) and decantation. Hexane extraction, though effective, is energy intensive and requires a large amount of capital investment. Decantation requires little capital investment and has the potential of being just as effective as hexane extraction.
Decantation, using centrifuges takes advantage of the density difference between the oil and the aqueous phase to create buoyant force on the oil suspended in solution. In order for the buoyant force to be strong enough to overcome the interfacial interactions and surface friction acting on the oil, individual oil droplets must be large enough so that sufficient force can be generated. The current horizontal decanters used in industry can separate particles as small as twenty micrometers in diameter. The success of current corn oil decantation is highly dependent on upstream processing conditions. Plants using high temperature, high or low pH, smaller grind, and long periods of retention tend to have increased oil yields.
However, there still exists a need for improved methods for recovering corn oil from byproducts of the dry-mill process used in the ethanol industry.